Estimating mixed layer nitrate in the North Atlantic Ocean

[摘要] Here we present an equation for the estimation of nitrate in surface watersof the North Atlantic Ocean (40° N to 52° N, 10° W to60° W). The equation was derived by multiple linear regression (MLR)from nitrate, sea surface temperature (SST) observational data and modelmixed layer depth (MLD) data. The observational data were taken from merchantvessels that have crossed the North Atlantic on a regular basis in 2002/2003and from 2005 to the present. It is important to find a robust and realisticestimate of MLD because the deepening of the mixed layer is crucial fornitrate supply to the surface. We compared model data from two models (FOAMand Mercator) with MLD derived from float data (using various criteria). TheMercator model gives a MLD estimate that is close to the MLD derived fromfloats. MLR was established using SST, MLD from Mercator, time and latitudeas predictors. Additionally a neural network was trained with the samedataset and the results were validated against both model data as a "groundtruth" and an independent observational dataset. This validation produced RMSerrors of the same order for MLR and the neural network approach. We concludethat it is possible to estimate nitrate concentrations with an uncertainty of±1.4 μmol L⁻¹ in the North Atlantic.

[学科分类] 地球化学与岩石